Hitherto, a toner for developing electrostatic images is produced by kneading under melting a mixture of a pigment such as carbon black, phthalocyanine blue, Carmine 6B, benzidine yellow, magnetite, etc., with a binder resin, after cooling, grinding the kneaded mixture, and classifying them into powders having sizes of from 5 to 25 .mu.m. For imparting necessary characteristics to toners, various additives are, if necessary, incorporated in the toners. For example, for controlling the level of the amount of triboelectricity generated at mixing toner and carrier, metal complex dyes, etc., are used. Also, for preventing papers from winding round a heat roll at fixing or the occurence of offset of paper at fixing, wax, etc., is added to toner at kneading under melting raw materials.
Also, since the form of toner is generally irregular and angular, a toner is usually poor in fluidity as powder. For improving the fluidity of toner powder, it has been frequently performed to dry-blend fine silica powders having primary particle size of from 10 .mu.m to 100 m with toner. A magnetic toner containing magnetic substance such as magnetitite, etc., in the toner particles is directly and magnetically attached to a development sleeve covering a magnet roll to form magnet brush. On the other hand, a non-magnetic toner, i.e., a toner containing no magnetic substance is mixed with magnetic substance particles of from 30 .mu.m to 200 .mu.m in particle size, called as "carrier", to form magnetic brush.
The resolutsion power of developed images, the density of solid black portions, and a gradation reproducibility greatly depend upon the characteristics of toner and carrier, in particular, the particle sizes thereof and smaller particle sizes give images having higher image quality. Recent high-image copying machines frequently employ carriers of small particle size. The particle size of commercially available ordinary toners is from 10 .mu.m to 12 .mu.m in volume average particle size but the use of a toner having the average particle size of about 8 .mu.m clearly improves image quality. It may be considered that the use of a toner having far smaller particle sizes can expect images of far higher image quality but when such a toner is actually prepared and used, it has been clarified that there are following problems.
(1) As the particle size of toner is smaller, the powder fluidity thereof becomes poorer. If the fluidity of toner is reduced, the toner forms bridges on a toner hopper to give hindrance for the supply of toner as well as the smoothness of the head of magnetic brush is reduced to form "haze" in images formed. In this case, the addition of a large amount of a fine hydrophobic silica powder as a fluidity improving agent may, as a matter of course, improve the fluidity of the toner but there occur troubles that the stability of the amount of tribo-charge is reduced and life of the developer is shortened.
(2) As the particle size of toner is smaller, the surface area thereof becomes larger and hence it is caused by the hygroscopicity of dyes or pigments exposed on the surface of the toner that the amount of tribo-charge is reduced and scattering of toner and the formation of fog are liable to occur at high humidity state.
(3) There is a limit in the dispersion of a dye or pigment for a resin and hence as the particle size of toner is smaller, very fine particles of uncovered carbon black or dye partially exist in the toner and partially exist on the surface of the toner in the attached state thereto. It is very difficult to remove these very fine particles in a classification step of toner and hence the existence is liable to appear as fog of images.
In view of the above-described problems in conventional techniques, the inventors have investigated for discovering a process of producing fine colored polymer particles, which can be used as toner as they are without need of grinding, by suspension polymerization, that is, for discovering a process of producing a toner by suspension polymerization capable of providing toner particles having uniform spherical particle form without need of grinding step, said toner particles having improved fluidity and charging property, and giving improved image quality. As the result of the investigations, the inventors have succeeded in achieving the present invention as set forth hereinbelow.